1. Field of the Invention
The present invention relates to a color shadow mask assembly and, more particularly, to a color shadow mask assembly excellent in heat resistance and vibration resistance.
2. Description of the Prior Art
FIG. 1 is a sectional view of the main part of a conventional color cathode-ray tube. Generally, in a color cathode-ray tube 12, phosphor films 4 and a shadow mask assembly 15 are sequentially disposed. The phosphor films 4 are formed on the inner surface of a face panel 3 constituting the front surface portion of a bulb 2. The shadow mask assembly 15 is constituted by a shadow mask 16 and a frame 17 for supporting and fixing the shadow mask 16. Electron beams 11 emitted from an electron gun 9 disposed in the neck of the bulb 2 are deflected by a magnetic field formed by a deflecting yoke 10 to scan the phosphor films 4 through the shadow mask 16, thereby displaying an image.
Only the shadow mask assembly will be described to compare it with the present invention. As shown in FIG. 1, originally, the shadow mask 16 serves to select the three electron beams that have passed through respective electron beam passing holes 16d, such that they correctly land on the phosphor films 4 of three predetermined colors. Accordingly, this shadow mask 16 must always maintain a predetermined relationship with the phosphor films 4.
FIG. 2 is a perspective view of the shadow mask. The shadow mask 16 has an aperture region 16a and a non-aperture region 16b, both of which are formed of a curved surface. A skirt 16c is arranged in the periphery of the shadow mask 16. The large number of dot-like or rectangular electron beam passing holes 16d are formed in the aperture region 16a of the shadow mask 16 to pass the electron beams therethrough.
As shown in FIG. 1, the electron beams 11 that reach the phosphor films 4 through the electron beam passing holes 16d of the shadow mask 16 are merely about 15% to 25% the total electron beams emitted from the electron gun 9, and most of the remaining electron beams collide against the shadow mask 16 to heat it. When the temperature of the shadow mask 16 increases, the position of the shadow mask 16 relative to the phosphor films 4 changes due to thermal expansion, and the landing positions of the electron beams 11 on the three-color phosphor films 4 displace. When this positional displacement exceeds the upper limit of an allowable range, the purity of color is degraded.
FIGS. 3A and 3B are sectional views of the main part of the shadow mask assembly taken along the vertical direction. The shadow mask assembly 15 is integrally formed by welding the predetermined positions of the skirt 16c of the shadow mask 16 and the predetermined positions of a side wall 17a of the frame 17 with each other. In this case, the combinations of the shadow mask 16 and frame 17 include the inner mask type shown in FIG. 3A and the outer mask type shown in FIG. 3B.
According to the inner mask type, as shown in FIG. 3A, the skirt 16c of the shadow mask 16 is arranged to oppose the inner surface of the side wall 17a of the frame 17. According to the outer mask type, as shown in FIG. 3B, the skirt 16c of the shadow mask 16 is arranged to oppose the outer surface of the side wall 17a of the frame 17, which is opposite to the inner mask type.
In either of the inner mask type and the outer mask type described above, the skirt 16c of the shadow mask 16 and the side wall 17a of the frame 17 overlap each other, and thereafter the predetermined positions of the overlapping portions are fixed by welding. These two types have individual characteristic features. For example, in the inner mask type, although the aperture area is small, the contact area through which the skirt 16c of the shadow mask 16 inscribes the side wall 17a of the frame 17 is designed to be large, so that the vibration of the shadow mask 16 at the natural frequency is suppressed. Hence, this type stands vibration. In the outer mask type, the aperture area is large. When this advantage is seen on the other way round, however, this type is weak to vibration.
In the color shadow mask assembly described above, the fitting state between the shadow mask and the frame sometimes leads to degradation in purity of color due to the landing displacement caused by thermal expansion and degradation in quality of the screen due to heat or vibration.
The present invention has been made in view of the above problems, and has as its object to provide a color shadow mask assembly in which a means for increasing the aperture area and improving the heat resistance and vibration resistance is provided, so that the influences of heat and vibration to the shadow mask assembly are suppressed.
In order to achieve the above object, according to the present invention, there is provided a color shadow mask assembly comprising a shadow mask spaced apart from an inner surface of a face panel by a predetermined gap and having a curved surface, and a rectangular frame for supporting and fixing the shadow mask, the shadow mask and the frame being welded and integrally formed to fix a side wall of the frame to a skirt of the face panel, wherein the skirt alternately overlaps inner and outer surfaces of the side wall of the frame at opposite surfaces between the skirt of the shadow mask and the side wall of the frame.
According to the second aspect of the present invention, there is provided a color shadow mask assembly according to the first aspect wherein, in a structure in which the skirt alternately overlaps the inner and outer surfaces of the side wall of the frame, the skirt overlaps the outer surface of the side wall of the frame at four corners of the frame.
According to the third aspect of the present invention, there is provided a color shadow mask assembly according to the first aspect, wherein, in a structure in which the skirt alternately overlaps the inner and outer surfaces of the side wall of the frame, the skirt overlaps the outer surface of the side wall of the frame at a total of not less than five portions including four corners of the frame and at least one of four sides of the frame.
According to the fourth aspect of the present invention, there is provided a color shadow mask assembly according to the first aspect wherein, in a structure in which the skirt alternately overlaps the inner and outer surfaces of the side wall of the frame, the skirt overlaps the outer surface of the side wall of the frame at a total of eight portions including four corners and four sides of the frame.
According to the fifth aspect of the present invention, there is provided a color shadow mask assembly according to the first aspect, wherein the side wall of the frame is formed with recesses and projections.
As described above, in the shadow mask assembly according to the present invention, recesses and projections are formed at at least the four corners and four sides of the side wall of the frame. The skirt of the shadow mask is fitted and inserted between the four corners and the projecting sides. Thereafter, the predetermined portions of opposing surfaces between the skirt of the shadow mask and the side wall of the frame are fixed to each other by welding. Both the conventional outer mask type and inner mask type are employed to provide a compound type shadow mask having the advantages of the two types.
More specifically, in the shadow mask assembly according to the present invention, since the opposing surfaces between the skirt of the shadow mask and the side wall of the frame are alternately inscribed and circumscribed, influences caused by heat or vibration can be suppressed. As a result, a shadow mask assembly excellent in heat resistance and vibration resistance because of its structure and having a wide aperture region can be provided.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principles of the present invention are shown by way of illustrative examples.